This application relates to measurements of cell growth, and in particular in the presence of drugs or other growth affecting agents, when the cells with or without the agents are flowed through a fluid channel embedded in, or attached to, a resonant structure.
This disclosure in some embodiments teaches a method and a system for rapidly measuring the effect of antibiotics on the growth of a bacterial culture, as well as other applications related to the counting and/or determining the mass/size of particles in the mass range of a few femtograms and larger, in the presence of growth-affecting agents. The disclosure addresses a strong diagnostic need to assess antibiotic efficacy in at most a few hours. A bacteria culture, or other cell culture, suspended in a liquid broth, may be passed through a mechanically resonating structure such as a suspended microchannel of appropriate size. A plurality of individual microbes may be detected and, optionally, their mass measured, by the effect their mass has on the microchannel's resonant frequency as they pass through the channel, one by one. This effect is described in the art as a method of measuring particle characteristics such as mass and size (U.S. application Ser. No. 13/310,776 and related applications incorporated by reference) and forms the basis for certain commercial particle measurement instruments. Additionally, the flow rate and measured sample volume can be determined from the time of passage of the microbes through the resonant microchannel, or by independent measurements of flow rate. Thus, the culture's distribution of microbe mass and concentration (microbes per ml of culture medium) may be measured.
To determine growth rate, the culture may be sampled at intervals, typically a few minutes apart. In each such time interval, multiple microbes may be detected and measured, providing information about the current number concentration of the microbes and the distribution of their masses. Performing these measurements over successive time intervals reveals the time development of the concentration and microbe mass and gives a detailed profile of the culture's growth rate and characteristics.
The above measurements can be performed on cultures containing antibiotics of various types and concentrations. The response of the culture to a particular antibiotic mixture can be determined by comparing the culture growth rate to an “unexposed” culture (a “control” sample) containing no antibiotics. Microbes whose growth is inhibited by an antimicrobial will show growth well below that of the unexposed culture, whereas a microbe strain that is “resistant” to the antimicrobial will show robust growth. A simplified, endpoint version of the method compares the mass and concentration measurements of the unexposed culture and the antibiotic mixture at a specified time after the start of the cultures' growth.
Finally, the disclosure in some embodiments teaches how the effect of a number of antibiotics can be assessed in one measurement by sequentially sampling from different mixtures in successive time intervals, or by simultaneously measuring different mixtures by using multiple resonant mass detectors.
This method of monitoring growth rate and comparison of growth rate between samples can be generalized beyond bacteria to assess the growth rate of any living cells or microscopic organisms, such as fungi, protozoa, and mammalian cells, including cancerous cells, and to measure the effects of drugs on their growth rate.
In addition to drugs, the effects of other agents on cell growth can also be assessed by this method, including topical anti-infectives and bacteriocides, anti-bacterial soaps, fungicides, and cosmetics.
This method can also be used to assess growth rate in applications where the goal is to promote growth, rather than inhibit it. An example is a comparison of the effectiveness of nutrient broths designed to optimize growth of cell cultures used, for example, to produce proteins used in biotherapeutic drugs, or to maximize growth rate in cultures of algae used for biofuels.